We propose to carry out a comprehensive study of the lower excited states of DNA and its components, with ultimate applications to photochemistry of DNA and its photobiology, using pulsed (nanosecond) higly monochromatic UV excitation together with fast digital data acquisition and treatment. We shall determine (1) wavelength-resolved lifetimes (2) corrected total excitation and emission spectra (3) time-resolved spectra (4) polarisation anisotropy of fluorescences and phosphorescences characteristic of monomar components (i.e., major bases, nucleosides and nucleotides) over a wide range of temperatures. An entirely parallel set of experiments will be carried out on the emission (both fluorescences and phosphorescences) from monomer aggregates, dinucleoside phosphates, polynucleotides and various DNAs with the aim of resolving and characterizing excimer effects. Investigations will be carried out on crystalline materials where possible as well as in a variety of solvents. DNA samples will include oriented films prepared at the University of Stockholm. In this way we anticipate obtaining comprehensive data which will allow us to map out in detail the pathways of energy migration in DNA from the initial absorption act to the final loss of energy degradation, chemical change or emission of luminescence. Such information is fundamental to understanding the photochemical and photobiological effects of UV on DNA. This information is also necessary as part of a longer range plan to develop photochemical methods of selectivity damaging DNA and thus changing its genetic information in a controlled way.